diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for aeson-dependent-sum
+
+## 0.1.0.0 -- 2022-08-27
+
+* First version. Released on an unsuspecting world.
diff --git a/COPYING b/COPYING
new file mode 100644
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,674 @@
+ GNU GENERAL PUBLIC LICENSE
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+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+ 17. Interpretation of Sections 15 and 16.
+
+ If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+
+ Copyright (C)
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+ Copyright (C)
+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+.
+
+ The GNU General Public License does not permit incorporating your program
+into proprietary programs. If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License. But first, please read
+.
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,40 @@
+# aeson-dependent-sum
+
+[](https://builds.sr.ht/~jack/aeson-dependent-sum?)
+[](https://www.gnu.org/licenses/gpl-3.0.html)
+
+If you need to (de)serialise JSON from/to a dependent sum (from the
+[`dependent-sum`](https://hackage.haskell.org/package/dependent-sum)
+package), this library provides `newtype` wrappers which you can use
+with the
+[`-XDerivingVia`](https://downloads.haskell.org/ghc/latest/docs/users_guide/exts/deriving_via.html#extension-DerivingVia)
+language extension. You might want to do this if:
+
+* You want to be work with a real value representing the sum's "tag";
+ or
+* You want to take advantage of the `f` parameter provided by `DSum`.
+
+## Example
+
+```haskell
+data CharacterClass a where
+ Fighter :: CharacterClass Fighter
+ Rogue :: CharacterClass Rogue
+ Wizard :: CharacterClass Wizard
+
+-- From the "constraints-extras" package:
+$(deriveArgDict ''CharacterClass)
+-- From the "dependent-sum-template" package. Not required, but useful:
+$(deriveGShow ''CharacterClass)
+$(deriveGEq ''CharacterClass)
+$(deriveGCompare ''CharacterClass)
+
+-- The derived `FromJSON`/`ToJSON` instances work on JSON objects like this:
+-- {
+-- "class": "fighter", -- or "rogue", or "wizard"
+-- "data": { ... } -- the exact fields differ depending on the value at "class".
+-- }
+newtype Character = Character (DSum CharacterClass Identity)
+ deriving (FromJSON, ToJSON)
+ via (TaggedObjectInline "Character" "class" CharacterClass Identity)
+```
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/aeson-dependent-sum.cabal b/aeson-dependent-sum.cabal
new file mode 100644
--- /dev/null
+++ b/aeson-dependent-sum.cabal
@@ -0,0 +1,64 @@
+cabal-version: 2.2
+name: aeson-dependent-sum
+version: 0.1.0.0
+synopsis: JSON encoding/decoding for dependent-sum
+description:
+ Newtype wrappers around [Data.Dependent.Sum.DSum](https://hackage.haskell.org/package/dependent-sum),
+ for use with @-XDerivingVia@. These wrappers are helpful when
+ parsing JSON objects where certain keys determine the type of the
+ deserialised value.
+
+homepage: https://sr.ht/~jack/aeson-dependent-sum
+bug-reports: https://todo.sr.ht/~jack/aeson-dependent-sum
+license: GPL-3.0-or-later
+license-file: COPYING
+author: Jack Kelly
+maintainer: jack@jackkelly.name
+copyright: (c) 2022 Jack Kelly
+category: Network
+build-type: Simple
+extra-source-files:
+ CHANGELOG.md
+ README.md
+
+tested-with: GHC ==8.8.4 || ==8.10.7 || ==9.0.2 || ==9.2.4 || ==9.4.1
+
+library
+ hs-source-dirs: src
+ exposed-modules: Data.Aeson.Dependent.Sum
+ ghc-options: -Wall
+ build-depends:
+ , aeson >=2.0 && <2.2
+ , base >=4.9 && <4.18
+ , constraints-extras ^>=0.3.2.1
+ , dependent-sum ^>=0.7.1.0
+ , some ^>=1.0.0.3
+ , vector >=0.12.3.1 && <0.14
+
+ default-language: Haskell2010
+
+test-suite aeson-dependent-sum-tests
+ type: exitcode-stdio-1.0
+ main-is: Main.hs
+ other-modules: Data.Aeson.Dependent.SumTest
+ ghc-options: -Wall -threaded
+ build-tool-depends: tasty-discover:tasty-discover ^>=5.0
+ build-depends:
+ , aeson
+ , aeson-dependent-sum
+ , base
+ , bytestring >=0.10 && <0.12
+ , constraints-extras
+ , dependent-sum
+ , dependent-sum-template ^>=0.1.1.1
+ , hedgehog >=1.0.5 && <1.2
+ , tasty >=1.2.3 && <1.5
+ , tasty-hedgehog >=1.2.0.0 && <1.4
+ , tasty-hunit ^>=0.10.0.2
+
+ hs-source-dirs: test
+ default-language: Haskell2010
+
+source-repository head
+ type: git
+ location: https://git.sr.ht/~jack/aeson-dependent-sum
diff --git a/src/Data/Aeson/Dependent/Sum.hs b/src/Data/Aeson/Dependent/Sum.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Aeson/Dependent/Sum.hs
@@ -0,0 +1,459 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE KindSignatures #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+-- |
+-- Module : Data.Aeson.Dependent.Sum
+-- Description : newtype wrappers for dependent sums, for use with @-XDerivingVia@
+-- Copyright : (c) 2022 Jack Kelly
+-- License : GPL-3.0-or-later
+-- Maintainer : jack@jackkelly.name
+-- Stability : experimental
+-- Portability : non-portable
+--
+-- When reading/writing JSON, you sometimes want to handle structures
+-- where the value at one key determines the type of the entire
+-- record. (In OpenAPI, they are sometimes called [polymorphic
+-- structures](https://swagger.io/docs/specification/data-models/inheritance-and-polymorphism/)
+-- and are specified using a @oneOf@ schema with the
+-- @discriminator/propertyName@ keyword.)
+--
+-- A naive approach would use a sum-of-records, and either @aeson@'s
+-- built-in @anyclass@ deriving or a manual two-step parse:
+--
+-- @
+-- data Fighter = F { ... } deriving anyclass (FromJSON, ToJSON)
+-- data Rogue = R { ... } deriving anyclass (FromJSON, ToJSON)
+-- data Wizard = W { ... } deriving anyclass (FromJSON, ToJSON)
+--
+-- data Character = Fighter Fighter | Rogue Rogue | Wizard Wizard
+-- instance FromJSON Character where
+-- parseJSON = withObject \"Character\" $ \o ->
+-- charClass <- o .: "class" :: Parser Text
+-- case charClass of
+-- "fighter" -> do
+-- favouredWeapon <- o .: "favouredWeapon"
+-- attackBonus <- o .: "attackBonus"
+-- -- etc.
+-- @
+--
+-- This works, but sometimes you want to manipulate the tag itself as
+-- a first-class value. In these instances, the
+-- [@dependent-sum@](https://hackage.haskell.org/package/dependent-sum)
+-- library can help, and we can also use
+-- [@deriving via@](https://downloads.haskell.org/ghc/latest/docs/html/users_guide/exts/deriving_via.html#extension-DerivingVia)
+-- to derive JSON instances on the @Character@ newtype:
+--
+-- @
+-- data CharacterClass a where
+-- Fighter :: CharacterClass Fighter
+-- Rogue :: CharacterClass Rogue
+-- Wizard :: CharacterClass Wizard
+--
+-- -- From the "constraints-extras" package:
+-- \$(deriveArgDict ''CharacterClass)
+-- -- From the "dependent-sum-template" package. Not required, but useful:
+-- \$(deriveGShow ''CharacterClass)
+-- \$(deriveGEq ''CharacterClass)
+-- \$(deriveGCompare ''CharacterClass)
+--
+-- newtype Character = Character (DSum CharacterClass 'Data.Functor.Identity.Identity')
+-- deriving (FromJSON, ToJSON)
+-- via ('TaggedObjectInline' \"Character\" "class" CharacterClass 'Data.Functor.Identity.Identity')
+-- @
+--
+-- To derive JSON instances on @Character@, we need to provide
+-- 'FromJSON' and 'ToJSON' instances for the @CharacterClass@ tag as
+-- well as for each record type. The 'Data.Some.Some' wrapper from the
+-- [@some@](https://hackage.haskell.org/package/some) package lets us
+-- wrap @CharacterClass@ so that its kind matches what 'FromJSON'
+-- expects:
+--
+-- @
+-- instance FromJSON (Some CharacterClass) where
+-- parseJSON = withText \"CharacterClass\" $ \t ->
+-- case t of
+-- "fighter" -> pure $ Some Fighter
+-- "rogue" -> pure $ Some Rogue
+-- "wizard" -> pure $ Some Wizard
+-- @
+--
+-- The @newtype@s in this module implement several different
+-- encoding/decoding strategies which roughly parallel the ones in
+-- [@aeson@](https://hackage.haskell.org/package/aeson).
+module Data.Aeson.Dependent.Sum where
+
+import Data.Aeson
+ ( FromJSON (..),
+ FromJSONKey (..),
+ FromJSONKeyFunction (..),
+ Key,
+ ToJSON (..),
+ ToJSONKey (..),
+ ToJSONKeyFunction (..),
+ Value (..),
+ object,
+ withArray,
+ withObject,
+ withText,
+ (.:),
+ (.=),
+ )
+import qualified Data.Aeson.Encoding as E
+import qualified Data.Aeson.Key as K
+import qualified Data.Aeson.KeyMap as KM
+import Data.Aeson.Types (Parser)
+import Data.Coerce (coerce)
+import Data.Constraint.Extras (Has', has')
+import Data.Dependent.Sum (DSum (..))
+import Data.Foldable (asum)
+import Data.Kind (Type)
+import Data.Proxy (Proxy (..))
+import Data.Some (Some (..))
+import Data.String (fromString)
+import Data.Vector ((!))
+import qualified Data.Vector as V
+import GHC.TypeLits (KnownSymbol, Symbol, symbolVal)
+
+-- | Newtype for 'DSum's representing JSON objects where one field
+-- determines the "type" of the object, and all the other data fields
+-- are stored under a distinct key. Analogous to the
+-- 'Data.Aeson.TaggedObject' constructor in 'Data.Aeson.SumEncoding'.
+--
+-- To derive 'FromJSON' and 'ToJSON' instances for JSON like this:
+--
+-- @
+-- {
+-- "class": "fighter", -- or "rogue", or "wizard"
+-- "data": { ... } -- the exact fields differ depending on the value at "class".
+-- }
+-- @
+--
+-- You would derive the instance like this:
+--
+-- @
+-- newtype Character = Character ('DSum' CharacterClass 'Data.Functor.Identity.Identity')
+-- deriving (FromJSON, ToJSON)
+-- via (TaggedObject \"Character\" "class" "data" CharacterClass 'Data.Functor.Identity.Identity')
+-- @
+--
+-- @since 0.1.0.0
+newtype
+ TaggedObject
+ (typeName :: Symbol)
+ (tagKey :: Symbol)
+ (contentsKey :: Symbol)
+ (tag :: k -> Type)
+ (f :: k -> Type)
+ = TaggedObject (DSum tag f)
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol typeName,
+ KnownSymbol tagKey,
+ KnownSymbol contentsKey,
+ FromJSON (Some tag),
+ Has' FromJSON tag f
+ ) =>
+ FromJSON (TaggedObject typeName tagKey contentsKey tag f)
+ where
+ parseJSON = withObject (symbolVal $ Proxy @typeName) $ \o ->
+ o .: fromString (symbolVal (Proxy @tagKey)) >>= \(Some tag) ->
+ has' @FromJSON @f tag $
+ TaggedObject . (tag :=>)
+ <$> o .: fromString (symbolVal (Proxy @contentsKey))
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol tagKey,
+ KnownSymbol contentsKey,
+ ToJSON (Some tag),
+ Has' ToJSON tag f
+ ) =>
+ ToJSON (TaggedObject typeName tagKey contentsKey tag f)
+ where
+ toJSON (TaggedObject (tag :=> fa)) =
+ object
+ [ fromString (symbolVal (Proxy @tagKey)) .= Some tag,
+ has' @ToJSON @f tag $ fromString (symbolVal (Proxy @contentsKey)) .= fa
+ ]
+
+ toEncoding (TaggedObject (tag :=> fa)) =
+ E.pairs $
+ mconcat
+ [ fromString (symbolVal (Proxy @tagKey)) .= Some tag,
+ has' @ToJSON @f tag $
+ fromString (symbolVal (Proxy @contentsKey)) .= fa
+ ]
+
+-- | Newtype for 'DSum's representing JSON objects where one field
+-- determines the "type" of the object, and all the other data fields
+-- are stored at the same level.
+--
+-- To derive 'FromJSON' and 'ToJSON' instances for JSON like this:
+--
+-- @
+-- {
+-- "class": "wizard", -- or "fighter", or "rogue"
+-- -- These fields will differ depending on the value at "class".
+-- "frogsLegs": 42,
+-- "eyesOfNewt": 9001
+-- }
+-- @
+--
+-- You would derive the instance like this:
+--
+-- @
+-- newtype Character = Character ('DSum' CharacterClass 'Data.Functor.Identity.Identity')
+-- deriving (FromJSON, ToJSON)
+-- via (TaggedObjectInline \"Character\" "class" CharacterClass 'Data.Functor.Identity.Identity')
+-- @
+--
+-- @since 0.1.0.0
+newtype
+ TaggedObjectInline
+ (typeName :: Symbol)
+ (tagKey :: Symbol)
+ (tag :: k -> Type)
+ (f :: k -> Type)
+ = TaggedObjectInline (DSum tag f)
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol typeName,
+ KnownSymbol tagKey,
+ Has' FromJSON tag f,
+ FromJSON (Some tag)
+ ) =>
+ FromJSON (TaggedObjectInline typeName tagKey tag f)
+ where
+ parseJSON v = flip (withObject (symbolVal $ Proxy @typeName)) v $ \o ->
+ o .: fromString (symbolVal (Proxy @tagKey)) >>= \(Some tag) ->
+ has' @FromJSON @f tag $
+ TaggedObjectInline . (tag :=>) <$> parseJSON v
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol typeName,
+ KnownSymbol tagKey,
+ Has' ToJSON tag f,
+ ToJSON (Some tag)
+ ) =>
+ ToJSON (TaggedObjectInline typeName tagKey tag f)
+ where
+ toJSON (TaggedObjectInline (tag :=> fa)) = has' @ToJSON @f tag $
+ case toJSON fa of
+ Object o ->
+ Object $
+ KM.insert
+ (fromString (symbolVal (Proxy @tagKey)))
+ (toJSON $ Some tag)
+ o
+ _ ->
+ error $
+ symbolVal (Proxy @typeName) <> "#toJSON: did not serialise to Object"
+
+-- | Newtype for 'DSum's representing JSON objects where the object
+-- has exactly one key, and the name of that key one field determines
+-- the "type" of the object. All the other data fields are stored in
+-- the corresponding value. Analogous to the
+-- 'Data.Aeson.ObjectWithSingleField' constructor in
+-- 'Data.Aeson.SumEncoding'.
+--
+-- To derive 'FromJSON' and 'ToJSON' instances for JSON like this:
+--
+-- @
+-- {
+-- "wizard": { -- or "fighter", or "rogue"
+-- -- The contents of this object will differ depending on the key.
+-- "frogsLegs": 42,
+-- "eyesOfNewt": 9001
+-- }
+-- }
+-- @
+--
+-- You would derive the instance like this:
+--
+-- @
+-- newtype Character = Character ('DSum' CharacterClass 'Data.Functor.Identity.Identity')
+-- deriving (FromJSON, ToJSON)
+-- via (ObjectWithSingleField \"Character\" CharacterClass 'Data.Functor.Identity.Identity')
+-- @
+--
+-- If the 'FromJSONKey'/'ToJSONKey' instances for @'Some' tag@ encode
+-- to something other than a JSON string, then a two-element array
+-- will be parsed/generated instead, like in 'TwoElemArray'.
+--
+-- @since 0.1.0.0
+newtype
+ ObjectWithSingleField
+ (typeName :: Symbol)
+ (tag :: k -> Type)
+ (f :: k -> Type)
+ = ObjectWithSingleField (DSum tag f)
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol typeName,
+ Has' FromJSON tag f,
+ FromJSONKey (Some tag)
+ ) =>
+ FromJSON (ObjectWithSingleField typeName tag f)
+ where
+ parseJSON j =
+ case tagParser of
+ Left valueParser ->
+ asum
+ [ parseArray valueParser j,
+ parseObject valueParser j,
+ fail $
+ unwords
+ [ "Cannot parse",
+ typeName,
+ "into a dependent sum: not an object or array"
+ ]
+ ]
+ Right keyParser -> parseObject (liftKeyParser keyParser) j
+ where
+ typeName = symbolVal $ Proxy @typeName
+
+ tagParser = case fromJSONKey @(Some tag) of
+ FromJSONKeyCoerce -> Right $ pure . coerce . K.toText
+ FromJSONKeyText fromText -> Right $ pure . fromText . K.toText
+ FromJSONKeyTextParser parseText -> Right $ parseText . K.toText
+ FromJSONKeyValue valueParser -> Left valueParser
+
+ liftKeyParser :: (Key -> Parser a) -> Value -> Parser a
+ liftKeyParser f = withText "Key" (f . K.fromText)
+
+ parseArray ::
+ (Value -> Parser (Some tag)) ->
+ Value ->
+ Parser (ObjectWithSingleField typeName tag f)
+ parseArray keyParser = withArray typeName $ \a ->
+ case V.length a of
+ 2 -> do
+ Some tag <- keyParser $ a ! 0
+ has' @FromJSON @f tag $
+ ObjectWithSingleField . (tag :=>) <$> parseJSON (a ! 1)
+ n ->
+ fail $
+ unwords
+ [ "Cannot unpack array of length",
+ show n,
+ "into a dependent sum"
+ ]
+
+ parseObject ::
+ (Value -> Parser (Some tag)) ->
+ Value ->
+ Parser (ObjectWithSingleField typeName tag f)
+ parseObject keyParser = withObject typeName $ \o ->
+ case KM.toList o of
+ [] -> fail "Empty object"
+ [(k, v)] -> do
+ Some tag <- keyParser . String $ K.toText k
+ has' @FromJSON @f tag $
+ ObjectWithSingleField . (tag :=>) <$> parseJSON v
+ _ ->
+ fail $
+ unwords
+ [ "Cannot unpack object with",
+ show . length $ KM.keys o,
+ "into a dependent sum"
+ ]
+
+-- | @since 0.1.0.0
+instance
+ ( Has' ToJSON tag f,
+ ToJSONKey (Some tag)
+ ) =>
+ ToJSON (ObjectWithSingleField typeName tag f)
+ where
+ toJSON (ObjectWithSingleField (tag :=> fa)) = has' @ToJSON @f tag $
+ case toJSONKey @(Some tag) of
+ ToJSONKeyText toKey _ -> object [toKey (Some tag) .= fa]
+ ToJSONKeyValue toValue _ -> case toValue (Some tag) of
+ String t -> object [K.fromText t .= fa]
+ v -> toJSON [v, toJSON fa]
+
+ toEncoding (ObjectWithSingleField (tag :=> fa)) = has' @ToJSON @f tag $
+ case toJSONKey @(Some tag) of
+ ToJSONKeyText _ toKeyEncoding ->
+ E.pairs (E.pair' (toKeyEncoding (Some tag)) (toEncoding fa))
+ ToJSONKeyValue toValue _ -> case toValue (Some tag) of
+ String t -> E.pairs (E.pair' (E.text t) (toEncoding fa))
+ v -> toEncoding [v, toJSON fa]
+
+-- | Newtype for 'DSum's representing serialisation to/from a
+-- two-element array. The @tag@ is stored in the first elemnt, and the
+-- serialised value is stored in the second. Analogous to the
+-- 'Data.Aeson.TwoElemArray' constructor in 'Data.Aeson.SumEncoding'.
+--
+-- To derive 'FromJSON' and 'ToJSON' instances for JSON like this:
+--
+-- @
+-- [
+-- "wizard", -- or "fighter", or "rogue"
+-- -- The contents of this object will differ depending on the previous element.
+-- {
+-- "frogsLegs": 42,
+-- "eyesOfNewt": 9001
+-- }
+-- ]
+-- @
+--
+-- You would derive the instance like this:
+--
+-- @
+-- newtype Character = Character ('DSum' CharacterClass 'Data.Functor.Identity.Identity')
+-- deriving (FromJSON, ToJSON)
+-- via (TwoElemArray \"Character\" CharacterClass 'Data.Functor.Identity.Identity')
+-- @
+--
+-- @since 0.1.0.0
+newtype
+ TwoElemArray
+ (typeName :: Symbol)
+ (tag :: k -> Type)
+ (f :: k -> Type)
+ = TwoElemArray (DSum tag f)
+
+-- | @since 0.1.0.0
+instance
+ ( KnownSymbol typeName,
+ Has' FromJSON tag f,
+ FromJSON (Some tag)
+ ) =>
+ FromJSON (TwoElemArray typeName tag f)
+ where
+ parseJSON = withArray (symbolVal (Proxy @typeName)) $ \a ->
+ case V.length a of
+ 2 -> do
+ Some tag <- parseJSON $ a ! 0
+ has' @FromJSON @f tag $
+ TwoElemArray . (tag :=>) <$> parseJSON (a ! 1)
+ n ->
+ fail $
+ unwords
+ [ "Cannot unpack array of length",
+ show n,
+ "into a dependent sum"
+ ]
+
+-- | @since 0.1.0.0
+instance
+ ( Has' ToJSON tag f,
+ ToJSON (Some tag)
+ ) =>
+ ToJSON (TwoElemArray typeName tag f)
+ where
+ toJSON (TwoElemArray (tag :=> fa)) =
+ has' @ToJSON @f tag $ toJSON [toJSON $ Some tag, toJSON fa]
+
+ toEncoding (TwoElemArray (tag :=> fa)) =
+ has' @ToJSON @f tag $ toEncoding [toJSON $ Some tag, toJSON fa]
diff --git a/test/Data/Aeson/Dependent/SumTest.hs b/test/Data/Aeson/Dependent/SumTest.hs
new file mode 100644
--- /dev/null
+++ b/test/Data/Aeson/Dependent/SumTest.hs
@@ -0,0 +1,411 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DerivingVia #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module Data.Aeson.Dependent.SumTest where
+
+import Data.Aeson
+ ( FromJSON (..),
+ FromJSONKey (..),
+ ToJSON (..),
+ ToJSONKey (..),
+ eitherDecode',
+ encode,
+ object,
+ withObject,
+ withText,
+ (.:),
+ (.=),
+ )
+import Data.Aeson.Dependent.Sum
+import Data.ByteString.Lazy (ByteString)
+import Data.Constraint.Extras (ArgDict)
+import Data.Constraint.Extras.TH (deriveArgDict)
+import Data.Dependent.Sum (DSum, (==>))
+import Data.Functor.Identity (Identity)
+import Data.GADT.Compare.TH (deriveGEq)
+import Data.GADT.Show.TH (deriveGShow)
+import Data.Some (Some (..), foldSome, mapSome, withSome)
+import GHC.Generics (Generic)
+import Hedgehog (Gen, Property, forAll, property, tripping)
+import qualified Hedgehog.Gen as Gen
+import qualified Hedgehog.Range as Range
+import Test.Tasty (TestName, TestTree, testGroup)
+import Test.Tasty.HUnit (testCase, (@?=))
+
+data CharacterClass a where
+ Fighter :: CharacterClass Fighter
+ Rogue :: CharacterClass Rogue
+ Wizard :: CharacterClass Wizard
+
+instance FromJSON (Some CharacterClass) where
+ parseJSON = withText "CharacterClass" $ \t -> case t of
+ "fighter" -> pure $ Some Fighter
+ "rogue" -> pure $ Some Rogue
+ "wizard" -> pure $ Some Wizard
+ _ -> fail $ "Unexpected CharacterClass: " <> show t
+
+instance ToJSON (Some CharacterClass) where
+ toJSON = foldSome $ \case
+ Fighter -> "fighter"
+ Rogue -> "rogue"
+ Wizard -> "wizard"
+
+deriving anyclass instance FromJSONKey (Some CharacterClass)
+
+deriving anyclass instance ToJSONKey (Some CharacterClass)
+
+data Fighter = F
+ { favouredWeapon :: String,
+ attackBonus :: Int
+ }
+ deriving stock (Eq, Show, Generic)
+ deriving anyclass (FromJSON, ToJSON)
+
+data Rogue = R
+ { sneakiness :: Int,
+ skills :: [String]
+ }
+ deriving stock (Eq, Show, Generic)
+ deriving anyclass (FromJSON, ToJSON)
+
+data Wizard = W
+ { frogsLegs :: Int,
+ eyesOfNewt :: Int,
+ darkPatron :: String
+ }
+ deriving stock (Eq, Show, Generic)
+ deriving anyclass (FromJSON, ToJSON)
+
+-- This has to be after the individual class records, as GHC cannot
+-- look beyond the splices.
+$(deriveArgDict ''CharacterClass)
+$(deriveGEq ''CharacterClass)
+$(deriveGShow ''CharacterClass)
+
+-- Newtype with contrived FromJSONKey/ToJSONKey instances to test
+-- non-string encoding/decoding.
+newtype NonStringKeyCharacterClass a
+ = NonStringKeyCharacterClass (CharacterClass a)
+ deriving newtype (ArgDict c)
+
+instance FromJSON (Some NonStringKeyCharacterClass) where
+ parseJSON =
+ withObject "NonStringKeyCharacterClass" $ \o ->
+ mapSome NonStringKeyCharacterClass <$> o .: "class"
+
+instance ToJSON (Some NonStringKeyCharacterClass) where
+ toJSON (Some (NonStringKeyCharacterClass c)) =
+ object ["class" .= Some c]
+
+instance FromJSONKey (Some NonStringKeyCharacterClass)
+
+instance ToJSONKey (Some NonStringKeyCharacterClass)
+
+newtype CharacterTaggedObjectInline = CharacterTaggedObjectInline (DSum CharacterClass Identity)
+ deriving stock (Eq, Show)
+ deriving
+ (FromJSON, ToJSON)
+ via (TaggedObjectInline "Character" "class" CharacterClass Identity)
+
+newtype CharacterTaggedObject = CharacterTaggedObject (DSum CharacterClass Identity)
+ deriving stock (Eq, Show)
+ deriving
+ (FromJSON, ToJSON)
+ via (TaggedObject "Character" "class" "data" CharacterClass Identity)
+
+newtype CharacterObjectWithSingleField = CharacterObjectWithSingleField (DSum CharacterClass Identity)
+ deriving stock (Eq, Show)
+ deriving
+ (FromJSON, ToJSON)
+ via (ObjectWithSingleField "Character" CharacterClass Identity)
+
+newtype CharacterObjectWithSingleDodgyField = CharacterObjectWithSingleDodgyField (DSum CharacterClass Identity)
+ deriving stock (Eq, Show)
+ deriving
+ (FromJSON, ToJSON)
+ via (ObjectWithSingleField "Character" NonStringKeyCharacterClass Identity)
+
+newtype CharacterTwoElemArray = CharacterTwoElemArray (DSum CharacterClass Identity)
+ deriving stock (Eq, Show)
+ deriving
+ (FromJSON, ToJSON)
+ via (TwoElemArray "Character" CharacterClass Identity)
+
+-- Unit Tests --
+
+test_DecodeTaggedObjectInline :: TestTree
+test_DecodeTaggedObjectInline =
+ makeParseTests
+ "DecodeTaggedObjectInline"
+ taggedObjectInlineJson
+ CharacterTaggedObjectInline
+
+test_DecodeTaggedObject :: TestTree
+test_DecodeTaggedObject =
+ makeParseTests
+ "DecodeTaggedObject"
+ taggedObjectJson
+ CharacterTaggedObject
+
+test_DecodeObjectWithSingleField :: TestTree
+test_DecodeObjectWithSingleField =
+ makeParseTests
+ "ObjectWithSingleField"
+ objectWithSingleFieldJson
+ CharacterObjectWithSingleField
+
+test_DecodeObjectWithSingleDodgyField :: TestTree
+test_DecodeObjectWithSingleDodgyField =
+ makeParseTests
+ "ObjectWithSingleDodgyField"
+ objectWithSingleDodgyFieldJson
+ CharacterObjectWithSingleDodgyField
+
+test_DecodeTwoElemArray :: TestTree
+test_DecodeTwoElemArray =
+ makeParseTests
+ "TwoElemArray"
+ twoElemArrayJson
+ CharacterTwoElemArray
+
+makeParseTests ::
+ (Eq a, FromJSON a, Show a) =>
+ TestName ->
+ (forall x. CharacterClass x -> ByteString) ->
+ (DSum CharacterClass Identity -> a) ->
+ TestTree
+makeParseTests label jsonFor wrap =
+ testGroup
+ label
+ [ testCase "fighter" $
+ eitherDecode' (jsonFor Fighter)
+ @?= Right (wrap $ expectedParses Fighter),
+ testCase "rogue" $
+ eitherDecode' (jsonFor Rogue)
+ @?= Right (wrap $ expectedParses Rogue),
+ testCase "wizard" $
+ eitherDecode' (jsonFor Wizard)
+ @?= Right (wrap $ expectedParses Wizard)
+ ]
+
+expectedParses :: CharacterClass a -> DSum CharacterClass Identity
+expectedParses = \case
+ Fighter ->
+ Fighter
+ ==> F
+ { favouredWeapon = "greatsword",
+ attackBonus = 12
+ }
+ Rogue ->
+ Rogue
+ ==> R
+ { sneakiness = 999,
+ skills = ["sneaking", "stealing", "lockpicking"]
+ }
+ Wizard ->
+ Wizard
+ ==> W
+ { frogsLegs = 42,
+ eyesOfNewt = 9001,
+ darkPatron = "Damo"
+ }
+
+taggedObjectInlineJson :: CharacterClass a -> ByteString
+taggedObjectInlineJson = \case
+ Fighter ->
+ "{\
+ \ \"class\": \"fighter\",\
+ \ \"favouredWeapon\": \"greatsword\",\
+ \ \"attackBonus\": 12\
+ \}"
+ Rogue ->
+ "{\
+ \ \"class\": \"rogue\",\
+ \ \"sneakiness\": 999,\
+ \ \"skills\": [\"sneaking\", \"stealing\", \"lockpicking\"]\
+ \}"
+ Wizard ->
+ "{\
+ \ \"class\": \"wizard\",\
+ \ \"frogsLegs\": 42,\
+ \ \"eyesOfNewt\": 9001,\
+ \ \"darkPatron\": \"Damo\"\
+ \}"
+
+taggedObjectJson :: CharacterClass a -> ByteString
+taggedObjectJson = \case
+ Fighter ->
+ "{\
+ \ \"class\": \"fighter\",\
+ \ \"data\": {\
+ \ \"favouredWeapon\": \"greatsword\",\
+ \ \"attackBonus\": 12\
+ \ }\
+ \}"
+ Rogue ->
+ "{\
+ \ \"class\": \"rogue\",\
+ \ \"data\": {\
+ \ \"sneakiness\": 999,\
+ \ \"skills\": [\"sneaking\", \"stealing\", \"lockpicking\"]\
+ \ }\
+ \}"
+ Wizard ->
+ "{\
+ \ \"class\": \"wizard\",\
+ \ \"data\": {\
+ \ \"frogsLegs\": 42,\
+ \ \"eyesOfNewt\": 9001,\
+ \ \"darkPatron\": \"Damo\"\
+ \ }\
+ \}"
+
+objectWithSingleFieldJson :: CharacterClass a -> ByteString
+objectWithSingleFieldJson = \case
+ Fighter ->
+ "{\
+ \ \"fighter\": {\
+ \ \"favouredWeapon\": \"greatsword\",\
+ \ \"attackBonus\": 12\
+ \ }\
+ \}"
+ Rogue ->
+ "{\
+ \ \"rogue\": {\
+ \ \"sneakiness\": 999,\
+ \ \"skills\": [\"sneaking\", \"stealing\", \"lockpicking\"]\
+ \ }\
+ \}"
+ Wizard ->
+ "{\
+ \ \"wizard\": {\
+ \ \"frogsLegs\": 42,\
+ \ \"eyesOfNewt\": 9001,\
+ \ \"darkPatron\": \"Damo\"\
+ \ }\
+ \}"
+
+objectWithSingleDodgyFieldJson :: CharacterClass a -> ByteString
+objectWithSingleDodgyFieldJson = \case
+ Fighter ->
+ "[\
+ \ { \"class\": \"fighter\" },\
+ \ {\
+ \ \"favouredWeapon\": \"greatsword\",\
+ \ \"attackBonus\": 12\
+ \ }\
+ \]"
+ Rogue ->
+ "[\
+ \ { \"class\": \"rogue\" },\
+ \ {\
+ \ \"sneakiness\": 999,\
+ \ \"skills\": [\"sneaking\", \"stealing\", \"lockpicking\"]\
+ \ }\
+ \]"
+ Wizard ->
+ "[\
+ \ { \"class\": \"wizard\" },\
+ \ {\
+ \ \"frogsLegs\": 42,\
+ \ \"eyesOfNewt\": 9001,\
+ \ \"darkPatron\": \"Damo\"\
+ \ }\
+ \]"
+
+twoElemArrayJson :: CharacterClass a -> ByteString
+twoElemArrayJson = \case
+ Fighter ->
+ "[\
+ \ \"fighter\",\
+ \ {\
+ \ \"favouredWeapon\": \"greatsword\",\
+ \ \"attackBonus\": 12\
+ \ }\
+ \]"
+ Rogue ->
+ "[\
+ \ \"rogue\",\
+ \ {\
+ \ \"sneakiness\": 999,\
+ \ \"skills\": [\"sneaking\", \"stealing\", \"lockpicking\"]\
+ \ }\
+ \]"
+ Wizard ->
+ "[\
+ \ \"wizard\",\
+ \ {\
+ \ \"frogsLegs\": 42,\
+ \ \"eyesOfNewt\": 9001,\
+ \ \"darkPatron\": \"Damo\"\
+ \ }\
+ \]"
+
+-- Property Tests --
+
+genCharacterDSum :: Gen (DSum CharacterClass Identity)
+genCharacterDSum = do
+ let string :: Gen String
+ string = Gen.string (Range.linear 1 100) Gen.unicode
+ int :: Gen Int
+ int = Gen.int (Range.linear 1 100)
+ list :: Gen a -> Gen [a]
+ list = Gen.list (Range.linear 1 100)
+
+ someClass <- Gen.element [Some Fighter, Some Rogue, Some Wizard]
+ withSome someClass $ \case
+ Fighter ->
+ (Fighter ==>) <$> do
+ favouredWeapon <- string
+ attackBonus <- int
+ pure F {..}
+ Rogue ->
+ (Rogue ==>) <$> do
+ sneakiness <- int
+ skills <- list string
+ pure R {..}
+ Wizard ->
+ (Wizard ==>) <$> do
+ frogsLegs <- int
+ eyesOfNewt <- int
+ darkPatron <- string
+ pure W {..}
+
+hprop_TrippingTaggedObjectInline :: Property
+hprop_TrippingTaggedObjectInline = property $ do
+ ch <- forAll genCharacterDSum
+ tripping (CharacterTaggedObjectInline ch) encode eitherDecode'
+
+hprop_TrippingTaggedObject :: Property
+hprop_TrippingTaggedObject = property $ do
+ ch <- forAll genCharacterDSum
+ tripping (CharacterTaggedObject ch) encode eitherDecode'
+
+hprop_TrippingObjectWithSingleField :: Property
+hprop_TrippingObjectWithSingleField = property $ do
+ ch <- forAll genCharacterDSum
+ tripping (CharacterObjectWithSingleField ch) encode eitherDecode'
+
+hprop_TrippingObjectWithSingleDodgyField :: Property
+hprop_TrippingObjectWithSingleDodgyField = property $ do
+ ch <- forAll genCharacterDSum
+ tripping (CharacterObjectWithSingleDodgyField ch) encode eitherDecode'
+
+hprop_TrippingTwoElemArray :: Property
+hprop_TrippingTwoElemArray = property $ do
+ ch <- forAll genCharacterDSum
+ tripping (CharacterTwoElemArray ch) encode eitherDecode'
diff --git a/test/Main.hs b/test/Main.hs
new file mode 100644
--- /dev/null
+++ b/test/Main.hs
@@ -0,0 +1,1 @@
+{-# OPTIONS_GHC -F -pgmF tasty-discover #-}